Alma begins by setting up a contrast between the people in the city of Gideon and the people in the city of Zarahemla. Alma preached repentance to those in Zarahemla. In Gideon, he will preach the opposite.
Alma speaks of exceeding great joy in having been able to witness repentance in Zarahemla. He notes that such joy was the result of afflictions and sorrow that required that he preach strongly to them. Nevertheless, he declares that according to the Spirit of God, he will have joy over the people of Gideon, without the afflictions and sorrows.
What made the difference between the two cities? The people of Gideon were either the very ones who had been with King Limhi in the city of Lehi-Nephi or they were their children. Where Alma had to remind the people of Zarahemla of the power of God to deliver them from captivity (see Alma 5:3–4), the people of Gideon had lived through the experience. It was they who were in bondage and who had required a great change of heart in order to be sufficiently humbled before Jehovah to be released from that bondage. Their conversion was still fresh and powerful.
That contrasted with those in Zarahemla, whose salvation from the Lamanites in the land of Nephi was at least three, if not four, generations in the past.